Andrew Clark
4ea064eb09
* Change OffscreenInstance isHidden to bitmask The isHidden field of OffscreenInstance is a boolean that represents whether the tree is currently hidden. To implement resuable effects, we need to also track whether the passive effects are currently connected. So I've changed this field to a bitmask. No other behavior has changed in this commit. I'll update the effects behavior in the following steps. * Extract passive mount effects to separate functions I'm about to add a "reappear passive effects" function that will share much of the same code as commitPassiveMountEffectOnFiber. To minimize the duplicated code, I've extracted the shared parts into separate functions, similar to what I did for commitLayoutEffectOnFiber and reappearLayoutEffects. This may not save much on code size because Closure will likely inline some of it, anyway, but it makes it harder for the two paths to accidentally diverge. * Don't mount passive effects in a new hidden tree This changes the behavior of Offscreen so that passive effects do not fire when prerendering a brand new tree. Previously, Offscreen did not affect passive effects at all — only layout effects, which mount or unmount whenever the visibility of the tree changes. When hiding an already visible tree, the behavior of passive effects is unchanged, for now; unlike layout effects, the passive effects will not get unmounted. Pre-rendered updates to a hidden tree in this state will also fire normally. This is only temporary, though — the plan is for passive effects to act more like layout effects, and unmount them when the tree is hidden. Perhaps after a delay so that if the visibility toggles quickly back and forth, the effects don't need to remount. I'll implement this separately. * "Atomic" passive commit effects must always fire There are a few cases where commit phase logic always needs to fire even inside a hidden tree. In general, we should try to design algorithms that don't depend on a commit effect running during prerendering, but there's at least one case where I think it makes sense. The experimental Cache component uses reference counting to keep track of the lifetime of a cache instance. This allows us to expose an AbortSignal object that data frameworks can use to cancel aborted requests. These cache objects are considered alive even inside a prerendered tree. To implement this I added an "atomic" passive effect traversal that runs even when a tree is hidden. (As a follow up, we should add a special subtree flag so that we can skip over nodes that don't have them. There are a number of similar subtree flag optimizations that we have planned, so I'll leave them for a later refactor.) The only other feature that currently depends on this behavior is Transition Tracing. I did not add a test for this because Transition Tracing is still in development and doesn't yet work with Offscreen.
React · 
React is a JavaScript library for building user interfaces.
- Declarative: React makes it painless to create interactive UIs. Design simple views for each state in your application, and React will efficiently update and render just the right components when your data changes. Declarative views make your code more predictable, simpler to understand, and easier to debug.
- Component-Based: Build encapsulated components that manage their state, then compose them to make complex UIs. Since component logic is written in JavaScript instead of templates, you can easily pass rich data through your app and keep the state out of the DOM.
- Learn Once, Write Anywhere: We don't make assumptions about the rest of your technology stack, so you can develop new features in React without rewriting existing code. React can also render on the server using Node and power mobile apps using React Native.
Learn how to use React in your project.
Installation
React has been designed for gradual adoption from the start, and you can use as little or as much React as you need:
- Use Online Playgrounds to get a taste of React.
- Add React to a Website as a
<script>tag in one minute. - Create a New React App if you're looking for a powerful JavaScript toolchain.
You can use React as a <script> tag from a CDN, or as a react package on npm.
Documentation
You can find the React documentation on the website.
Check out the Getting Started page for a quick overview.
The documentation is divided into several sections:
You can improve it by sending pull requests to this repository.
Examples
We have several examples on the website. Here is the first one to get you started:
import { createRoot } from 'react-dom/client';
function HelloMessage({ name }) {
return <div>Hello {name}</div>;
}
const root = createRoot(document.getElementById('container'));
root.render(<HelloMessage name="Taylor" />);
This example will render "Hello Taylor" into a container on the page.
You'll notice that we used an HTML-like syntax; we call it JSX. JSX is not required to use React, but it makes code more readable and writing it feels like writing HTML. If you're using React as a <script> tag, read this section on integrating JSX; otherwise, the recommended JavaScript toolchains handle it automatically.
Contributing
The main purpose of this repository is to continue evolving React core, making it faster and easier to use. Development of React happens in the open on GitHub, and we are grateful to the community for contributing bugfixes and improvements. Read below to learn how you can take part in improving React.
Code of Conduct
Facebook has adopted a Code of Conduct that we expect project participants to adhere to. Please read the full text so that you can understand what actions will and will not be tolerated.
Contributing Guide
Read our contributing guide to learn about our development process, how to propose bugfixes and improvements, and how to build and test your changes to React.
Good First Issues
To help you get your feet wet and get you familiar with our contribution process, we have a list of good first issues that contain bugs that have a relatively limited scope. This is a great place to get started.
License
React is MIT licensed.